---
id: CVE-2020-3555
title: >-
  A vulnerability in the SIP inspection process of Cisco Adaptive Security
  Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software
  could allow an unauthenticated, remote attacker to cause a crash and reload of
  an affecte…
summary: >-
  A vulnerability in the SIP inspection process of Cisco Adaptive Security
  Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software
  could allow an unauthenticated, remote attacker to cause a crash and reload of
  an affecte…
severity: medium
cvss: 6.8
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H'
cwe:
  - CWE-404
  - CWE-404
vendor: cisco
product: adaptive_security_appliance
affected:
  - adaptive_security_appliance < 9.6.4.43
  - secure_firewall_threat_defense <= 6.2.2
  - 'secure_firewall_threat_defense >= 6.3.0, < 6.3.0.6'
  - 'secure_firewall_threat_defense >= 6.4.0, < 6.4.0.10'
  - 'secure_firewall_threat_defense >= 6.5.0, < 6.5.0.5'
  - secure_firewall_threat_defense = 6.6.0
  - 'adaptive_security_appliance_software >= 9.7.0, < 9.8.4.24'
  - 'adaptive_security_appliance_software >= 9.9.0, < 9.9.2.80'
  - 'adaptive_security_appliance_software >= 9.10.0, < 9.10.1.43'
  - 'adaptive_security_appliance_software >= 9.12.0, < 9.12.4.2'
  - 'adaptive_security_appliance_software >= 9.13.0, < 9.13.1.13'
  - 'adaptive_security_appliance_software >= 9.14.0, < 9.14.1.19'
patched:
  - adaptive_security_appliance 9.6.4.43
  - secure_firewall_threat_defense 6.5.0.5
  - adaptive_security_appliance_software 9.14.1.19
published: '2020-10-21'
updated: '2026-08-11'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2020-3555'
references:
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-sipdos-3DGvdjvg
    label: psirt@cisco.com
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-sipdos-3DGvdjvg
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.01681
epssPercentile: 0.75941
ingestedAt: '2026-08-11T19:48:28.809Z'
---

## Overview

A vulnerability in the SIP inspection process of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a crash and reload of an affected device, resulting in a denial of service (DoS) condition. The vulnerability is due to a watchdog timeout and crash during the cleanup of threads that are associated with a SIP connection that is being deleted from the connection list. An attacker could exploit this vulnerability by sending a high rate of crafted SIP traffic through an affected device. A successful exploit could allow the attacker to cause a watchdog timeout and crash, resulting in a crash and reload of the affected device.

## Affected

- `adaptive_security_appliance < 9.6.4.43`
- `secure_firewall_threat_defense <= 6.2.2`
- `secure_firewall_threat_defense >= 6.3.0, < 6.3.0.6`
- `secure_firewall_threat_defense >= 6.4.0, < 6.4.0.10`
- `secure_firewall_threat_defense >= 6.5.0, < 6.5.0.5`
- `secure_firewall_threat_defense = 6.6.0`
- `adaptive_security_appliance_software >= 9.7.0, < 9.8.4.24`
- `adaptive_security_appliance_software >= 9.9.0, < 9.9.2.80`
- `adaptive_security_appliance_software >= 9.10.0, < 9.10.1.43`
- `adaptive_security_appliance_software >= 9.12.0, < 9.12.4.2`
- `adaptive_security_appliance_software >= 9.13.0, < 9.13.1.13`
- `adaptive_security_appliance_software >= 9.14.0, < 9.14.1.19`

## Remediation

Upgrade past the affected range:

- `adaptive_security_appliance 9.6.4.43`
- `secure_firewall_threat_defense 6.5.0.5`
- `adaptive_security_appliance_software 9.14.1.19`